USB 2.0 seems very buggy on VirtualBox (I am using 1.6.4 on Mandriva). To get my Canon DSLR (XSI / 450D) to work, I had to disable USB 2.0 support. All EOS Utility functions work beautifully, including Remote Live View :-)

Software versions used:
Virtualbox 1.6.4 (disable USB 2.0)
Host OS: Mandriva 2008.1 (changed kernel to kernel-laptop-latest)
Guest OS: Windows XP Professional SP2 (with Guest Additions)
Canon Software from the disk (DPP, EOS Utility, etc.)
EOS Utility updated from Canon website

Hooray!